The purpose of this study centers on the development of technology for introducing an extra chromosome by micromanipulation into a fertilized mammalian ovum in order to produce trisomeric embryos. Initially mouse ova will be used until it is demonstrated that the extra chromosome will be accepted and will participate in division. Subsequently ova from Macaca species will be used and efforts will be concentrated on injecting ova with an extra Y chromosome. These ova will then be inserted into the uterus of a surrogate mother for further development and at various stages of embryonic and fetal development, the aneuploids can be removed and examined for morphological and biochemical differences. The concept of this study is based on the premise that the deleterious effects of an extra chromosome are incurred early in embryogenesis or during fetal development and that an animal model is necessary to investigate this area.